1. Field of the Invention
The present invention relates to, e.g., a pay broadcast system.
2. Description of the Related Art
As digitization is applied not only to communication satellite (CS) but also to cable TV and ground broadcast, digital broadcast is expected to provide advanced services and to play an important role in broadcast services.
The great feature of digital broadcast is to be able to largely increase the number of broadcast channels compared to analog broadcast, since the use efficiency of frequencies required to send programs can be improved due to introduction of information compression techniques. Furthermore, since a high-level error correction technique can be applied, high-quality, uniform services can be provided.
As a result of digitization, not only conventional video & audio broadcast but also text & data broadcast (data broadcast) are available. For example, news can be broadcasted as text data, and PC software can be delivered during broadcast. Systems for providing such services have appeared successively.
As receiver apparatuses, not only conventional floor models but also mobile receiver apparatuses such as a portable information terminal that can be used even when the user is on the move, a mobile terminal which is premised on use in an automobile and is equipped in the automobile have appeared.
In order to implement pay broadcast services in such system, customer management according to the reception term and contract contents must be made (for example, encrypted broadcast contents are sent, and are descrambled based on the contract contents). The customer management according to the reception term allows the user to watch programs on contract channels within the reception term specified by payment of a predetermined fee.
Key information used to descramble or decrypt in a receiver apparatus must be reliably provided to only right audience (according to the contract channels and reception term) upon preventing wrong audience.
To realize this, conventionally, a master key is prepared in each broadcast receiver apparatus, and contract information indicating a contract form that includes work keys of contract channels, viewable channel information, and the like is encrypted using the master key and is sent via a broadcast wave. Note that the work key is unique to a channel, and can decrypt a channel key of that channel, which is sent as encrypted data. The channel key is used to descramble (decrypt) the scrambled (encrypted) broadcast contents.
In such conditional access system, the work keys and contract information, which are encrypted using the master key (set for each receiver apparatus) correspond to conditional access information unique to the receiver apparatus, and channel keys encrypted using the work keys (common to a plurality of receiver apparatuses) correspond to common conditional access information.
Conventionally, even unique conditional access information is sent via a broadcast wave (which is unsuitable for sending individual information). Information for an individual subscriber unnecessarily occupies the transmission band since it is sent to all subscribers, and must be repetitively sent during a required period since information indicating whether or not that subscriber received the information cannot be obtained.
Furthermore, the work keys contained in individual conditional access information are set for each reception term (normally, one month), and a broadcast station must individually send those keys every reception term, and must repetitively send them for a predetermined period since a contract management center cannot detect if each receiver apparatus actually received that information. For this reason, individual conditional access information currently accounts for a large part of conditional access information.
On the other hand, CS broadcast or the like-provides a PPV (pay per view) service that charges a user a fee for a program that he or she watched. In order to allow a subscriber to watch a desired program immediately after audiovisual operation, the subscriber need not directly contact a contract management center upon audiovisual operation, but a reception history is stored in a receiver apparatus, and the center periodically repossesses the reception history. However, with such arrangement, if the subscriber knowingly or accidentally disconnects a public telephone network to which the center established connection to repossess the reception history, the center cannot repossess the reception history.